Mosquito behavior changes with the changing physiological state of the insect. Although host-seeking behavior is generally no longer expressed once a blood meal has been ingested and oogenesis has commenced, females do become more attracted to oviposition site stimuli at this time, and display what we have termed "pre-oviposition" behavior in search of a place to lay their eggs. Our laboratory has recently demonstrated that the behavioral switch from host-seeking to pre-oviposition can be induced in non-gravid mosquitoes by transfusing hemolymph from gravid donors. Based on our preliminary experiments, we postulate that in order to display pre-oviposition, a mosquito must first perceive oviposition sited stimuli, must have mature ovaries, and must be mated. An examination is proposed of the mechanisms by which these three factors communicate with the central nervous system of the mosquito. The time course for the presence of the humoral pre-oviposition factor and its stability will first be determined. Using techniques of microsurgery, the way in which mating influences this behavior and how pre- oviposition is terminated after oviposition will be determined. Because mosquitoes reared in the field are often marginally nourished, the possibility that pre-oviposition behavior can be modified by suboptimal nutritional state will be evaluated.